The present invention relates to breathing tube comprising a corrugated tube and a casing for reduction of heat transfer from the corrugated tube commonly utilized with recirculatory aided breathing circuits, and the ambient atmosphere. Briefly, the invention includes a tubular sleeve or casing which encloses an air impervious conduit inside the casing in such a manner that a dead air space is created between the outside of the conduit and the inside of the casing. The linear volume of the dead air space is approximately equal to the linear volume of the conduit it encompasses.
Various type tubular and conduit arrangements are presently in use for the maintenance of respiration and conditioning of the air supply to a patient. Such circuits are commonly used for the introduction of anesthesia during surgery and/or attached to respirators and/or other types of patient ventilation/breathing devices. A complete respiratory system usually includes a pressure generator (mechanical or manually powered), inhalation tube, exhalation tube, "Y" piece, and a means of attaching the inhalation and exhalation tubes to the patient, (i.e. by endotracheal catheter, or face mask, etc). The respirator then mechanically controls the flow of gases within the circuit which may also include humidifying and/or temperature adjusting devices interconnected with the circuit.
The traditional circuit is attached to the patient's airway opening via a Y-shaped connector. The arms of this "Y" connector are attached to inhalation and exhalation tubes and the respirations of the patient are controlled by the operator/respirator, (i.e. number of respirations per minute, volume of each respiration, etc).
When artificial ventilation of a patient is required over extended periods of time the inhalant should have an inspiration temperature within the range of normal body temperature and a relative humidity approaching 100% in order to minimize damage to the patients airway, aveoli, bronchiles and other parts of the lungs.
Often, in association with the traditional circuit, a combination of temperature-humidity control devices may be employed on the inhalation side of the circuit to attempt to assure that the optimum temperature and humidity conditions are maintained.
A common problem associated with traditional circuits is the distance between the inhalant source and humidifier-temperature control device and the respiratory passageway of the patient ventilated is quite long. The long distance that the inhalants must travel through the conduits, both to and from the humidifier-temperature control device frequently allows the inhalants to fall below the optimal temperature and humidity levels for such inhalants entering the patient's lungs. Thus, prolonged exposure may damage the lungs and also may lower the patient's body temperature below desirable levels.
Attempts have been made to alleviate the aforenoted problem associated with a traditional circuit by placing temperature-humidifier control devices in close proximity to the patient. However, because the traditional ciruit is already cumbersome, the addition of such devices at this point on the inhalation circuit cause most attendants and patients to find this configuration greatly annoying and inconvenient, and potentially dangerous.
In an attempt to alleviate the cumbersomeness of a traditional circuit, British Patent Publication No. 2,029,703A, discloses the use of a single limb anesthesia circuit consisting of two corrugated wall tubes, where each tube is affixed at one end to a respirator and at the other to a connector to the patient's airway. Because both inhalation and exhalation tubes were affixed to a connector on the patient side, the inner tube offered resistance and restricted the outer tube when pressure within the inner tube was increased, i.e. as with every forced inhalation by the respirator.
The previously discussed deficiencies of British Patent Publication No. 2,029,703A were attempted to be rectified in U.S. Pat. No. 4,463,755, to Suzuki. Suzuki defines an inner inhalation tube coaxially circumscribed by an outer exhalation tube, the resistance between the two tubes was minimized by retaining members affixed to the inner tube at a fixed distance. However, there are two major problems associated with a Suzuki-type circuit. First, they are expensive and second, there may be a build-up of liquid condensation and other matter within the exhalation tube which is caused by the difference in the temperature gradient between the patient's exhalant breath and the atmospheric temperature in contact with the exhalant tube.
Further, this condensation provides an environment for germicidal growth when used for prolonged periods. This germicidal growth can be re-aspirated in the lungs of the patient increasing the possibility of complicating infections which increase morbitity and mortality. The aforenoted disadvantageous condensation is commonly associated with almost all traditional breathing circuits.
Another prior art U.S. Pat. No. 4,232,667 to Chalon, et. al., discloses a single limb breathing circuit used for anesthesia introduction. The Chalon invention defines a closed circuit system consisting of an absorber container that removes CO.sub.2 from the circuit thereby permitting only Oxygen and anesthesia gasses to be continuously circulated within the system. The primary benefits disclosed in Chalon, et. al. are reduced anesthesia costs because the anesthesia unabsorbed by the lungs is recirculated to the patent. Thus, less anesthesia is needed for the operation and there is a lower probability of operating room explosions due to the absence of highly volatile anesthestic gasses being exhaled from the patient and released into the operating room. However, Chalon suffers from the same disadvantages as Suzuki.
U.S. Pat. No. 3,814,091 to Henkin teaches a breathing apparatus using a corrugated breathing tube with a flexible tubular enclosure surrounding a portion of the breathing tube but, contrary to the present invention where there is no air flow between the hose and the envelope, in Henkin flow conduits or holes are required in the breathing tube to allow air flow into the space between the breathing tube and the envelopes. Consequently, the area between the breathing tube and the tubular enclosure (envelope) of Henkin is not a dead air space, and therefore not insulating as it is in the present invention. In Henkin the outer tube enclosure acts like a balloon which when squeezed by the operator delivers a volume of air to the patient's air stream. Moreover in Henkin, the outer envelope may contain a slit to act as a pressure relief means.
U.S. Pat. No. 2,119,446 like U.S. Pat. No. 3,814,091 relates to a perforated corrugated tube which is surrounded by a balloon.
U.S. Pat. No. 4,269,193 teaches a breathing apparatus with concentric air flow tubes where air flows through the annular area so the area is not a dead air space as provided by the present invention. Moreover, the air flowing in the outer tube is subject to uninhibited cooling and condensation which is sought to be prevented by the present invention.
U.S. Pat. No. 4,300,547 teaches an inhalation conduit which is covered with a sheath of material which can be wetted with a liquid so the conduit is cooled by evaporation.
Likewise U.S. Pat. No. 3,924,619 teaches a heat exchange means not an insulating arrangement for breathing conduits.
U.S. Pat. No. 3,185,182 to Waddell relates to a conduit having a corrugated tubular body with a plastic coated circumferential reinforcement containing an additional reinforcement member. The tube does not have a dead air insulating space.
U.S. Pat. No. 3,490,496 to Stearns relates to flexible transfer lines for cryogenic liquids. The coaxial tubing has inner and outer concentrically arranged tubes and spacing means therebetween.
U.S. Pat. No. 2,898,941 to Kilcup provides an inhaler tube having exterior helical corrugations to import maximum flexibility while at the same time maintaining the tube free from kinking with the tube also having a smooth interior surface that readily lends itself to thorough cleansing and sterilization.
U.S. Pat. No. 3,858,615 to Weigl describes a kink-resistant hose construction of a one piece tube of flexible material having a smooth cylindrical inner wall surface for efficient air flow and easy cleaning and having axially spaced concentric rings on its outer wall.
U.S. Pat. No. 4,000,341 to Matson refers to a autoclavable corrugated respiratory air tubing which is translucent so that liquid build-up in the tubing can be seen through the walls of the tubing.
U.S. Pat. No. 2,073,335 to Connell is a breathing tube which employs various reinforcements which may be applied by hand or by suitable mechanical means.
U.S. Pat. No. 4,415,389 to Medford suggests an inner corrugated hose construction and a sleeve disposed around the hose having the function of improving the fluid pressure resistance and the external water resistance, the sleeve being taut and free of sags.
U.S. Pat. No. 4,007,737 to Paluch relates to a anesthesia breathing circuit having inner and outer tubes with spacer means for supporting and maintaining the tubes enspaced in relatively fixed spacial relation.
Also insulating ventilation hoses is suggested by Drs. Alan R. Mizutani, Ozahi, and Rusk in ANESTH ANALG. 1991,72:561-7.